Carbon capture solvents and methods for using such solvents

ABSTRACT

A solvent for recovery of carbon dioxide from gaseous mixture, having alkanolamine, reactive amines acting as promoter or activators, glycol, and a carbonate buffer. A solvent for recovery of carbon dioxide from gaseous mixture, having alkanolamine, reactive amines acting as promoter or activators, sulfolane, and a carbonate buffer. One specific solvent contains less than about 75% by weight of water and has a single liquid phase.

STATEMENT OF RELATED APPLICATIONS

This patent application claims the benefit of U.S. provisional patentapplication No. 61/759,191 having a filing date of Jan. 31, 2013, whichis incorporated herein in its entirety by this reference.

BACKGROUND

This disclosure relates to a method for the preparation of solvents andmethods for treatment of industrial effluent gases, and, morespecifically, this disclosure relates to solvents and process for usingthese solvents to aid in the removal of carbon dioxide (CO₂) from othersources such as power plants or industrial utility.

SUMMARY

This disclosure is directed towards a solvent for recovery of carbondioxide from gaseous mixture having an alkanolamine, reactive aminesacting as promoter or activators, and a carbonate buffer. One specificsolvent contains less than about 75% by weight of dissolving mediumwater and glycol (e.g., polyethylene glycol) and has a single liquidphase. Another specific solvent contains less than about 75% by weightof dissolving medium water and glycol (e.g., polyethylene glycol) andhas a single liquid phase. Another specific solvent contains less thanabout 75% by weight of dissolving medium water and sulfolane and has asingle liquid phase.

Additional features of the disclosure will become apparent to thoseskilled in the art upon consideration of the following detaileddescription of illustrative embodiments exemplifying the best mode ofcarrying out the disclosure as presently perceived.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the accompanying figuresin which:

FIG. 1 is a schematic picture of the reaction; and

FIG. 2 is a perspective view of one illustrative embodiment.

FIG. 3 shows a viscosity plot of one exemplary solvent.

DEFINITIONS

As used herein, the term “solvent” can refer to a single solvent or amixture of solvents.

DETAILED DESCRIPTION

This disclosure includes several aspects and provides methods andsolvents that, when used alone or in combination, may significantlyreduce or eliminate carbon dioxide (CO₂) emissions from industrialplants that burn solid fuels, particularly coal-fired power plants. Thisdisclosure is directed to CO₂ capture/sequestration from flue gases CO₂emissions should also be applicable to CO₂ capture from gas and oilfired boilers, combined cycle power plants, coal gasification, andhydrogen plants, biogas plants.

As shown in FIG. 1, the vapor and liquid phases are contact in a smallcross-section. In treating the emissions, the absorption step involvesremoval of acid gases and other components from the gas phase bytransport into the liquid phase. The gas-liquid interface separates thephases. An absorbing gas dissolves into the liquid at the interface,then diffuses across a thin layer of liquid (termed the diffusion layer)of one specific solvent. As it diffuses, the gas meets the reactiveabsorbent component in one specific solvent, reacts with it, andgenerates heat and reaction products such as carbonate. Reactionproducts can diffuse into the bulk liquid while the liberated heat ofreaction heats the liquid. In one example, there is a mixture oftertiary amine/hindered amine, reactive amines (e.g, a polyamineactivator), carbonate buffer, a dissolving medium of water and physicalpolyethylene glycol as to solvent system remain as a single liquid phasein removing acidic gases from gaseous mixture.

In embodiment, one specific solvent for absorbing CO₂ includesalkanolamines, which can be any one of compounds represented byfollowing formulae (I) to (III) or a mixture thereof:

in the formulae (I) to (III): x and y respectively satisfy relationship:1 less than or equal to 5 and 2 less than or equal to 10; and R¹, R²,R³, and R⁴ represent—C_(i)H_(j)O_(k)N_(l) (where i=0 to 10, j=1 to 21,k=0 to 5, and l=0 to 5).

In one illustrative solvent, reactive amines can be any one of nitrogencontaining compounds represented by following formulae (IV) to (XIII) ormixture thereof. Reactive amines may be nitrogen-containing compoundhaving a secondary nitrogen in a ring or a nitrogen-containing compoundhaving a tertiary nitrogen in a ring.

In another illustrative solvent, reactive amines can be anitrogen-containing compound having secondary and tertiary nitrogen in aring.

In another illustrative solvent, reactive amines can be anitrogen-containing compound having a nitrogen in a substituent groupbranching from the ring.

In another illustrative solvent, reactive amines can benitrogen-containing compound may be a nitrogen-containing compoundhaving a primary nitrogen in a substituent group branching from thering.

In another illustrative solvent, reactive amines can be anitrogen-containing compound having three nitrogen atoms or more in amolecule thereof.

In another illustrative solvent, reactive amines can be anitrogen-containing compound having in a molecule thereof all ofprimary, secondary, and tertiary nitrogens.

in the formulae (IV) to (V): R⁵ and R⁶ represent—C_(i)H_(j)O_(k)N_(l)(where i=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R⁷ and R⁸represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5),

in the formula (VI): R⁹ and R¹¹ represent—C_(i)H_(j)O_(k)N_(l) (wherei=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R10represents—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5),

in the formula (VII): R⁹ and R¹¹ represent—C_(i)H_(j)O_(k)N_(l) (wherei=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R¹° and R¹²represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5),

in the formula (VIII): R⁹ represents—C_(i)H_(j)O_(k)N_(l) (where i=0 to10, j=0 to 26, k=0 to 5, and l=0 to 5); and R¹³, R¹⁴, R¹⁵ and R¹⁶represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5),

in the formula (IX): R9 and R18 represent—C_(i)H_(j)O_(k)N_(l) (wherei=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R10, R15 and R17represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5),

in the formula (X): R⁹ represents—C_(i)H_(j)O_(k)N_(l) (where i=0 to 10,j=0 to 26, k=0 to 5, and l=0 to 5); and R¹³, R¹⁴, R¹⁶ and R¹⁹represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5),

in the formula (XI): R⁹ and R¹⁸ represent—C_(i)H_(j)O_(k)N_(l) (wherei=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R¹⁴, R¹⁷ and R²°represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5),

in the formula (XII): R⁹ and R²¹ represent—C_(i)H_(j)O_(k)N_(l) (wherei=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R¹⁴, R¹⁶ and R¹⁷represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5),

in the formula (XIII): R⁹ and R¹⁸ represent—C_(i)H_(j)O_(k)N_(l) (wherei=0 to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R¹⁴, R¹⁶ and R¹⁷represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5).

In one specific solvent, the second compound component may be any one ofnitrogen-containing compounds represented by following formulae (XIV) to(XIX) or a mixture thereof:

in the formula (XIV): R²² represents—C_(i)H_(j)O_(k)N_(l) (where i=0 to10, j=0 to 26, k=0 to 5, and l=0 to 5); and R²³ and R²⁴represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5),

in the formula (XV): R²⁵ represents—C_(i)H_(j)O_(k)N_(l) (where i=0 to10, j=0 to 26, k=0 to 5, and l=0 to 5); and R23 and R²⁶represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5),

in the formula (XVI): R²³, R²⁷ and R²⁸ represent—C_(i)H_(j)O_(k)N_(l)(where i=1 to 10, j=0 to 26, k=0 to 5, and l=0 to 5),

in the formula (XVII): R²² represents—C^(i)H^(j)O^(k)N^(l) (where i=0 to10, j=0 to 26, k=0 to 5, and l=0 to 5); and R²³, R²⁴, R²⁷ and R²⁹represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5),

in the formula (XVIII): R²⁵ represents—C_(i)H_(j)O_(k)N_(l) (where i=0to 10, j=0 to 26, k=0 to 5, and l=0 to 5); and R²³, R²⁶ and R²⁹represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5),

in the formula (XIX): R²³, R²⁷, R²⁸ and R²⁹represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5)

In one specific solvent, the reactive amine may be a nitrogen-containingcompound represented by following formula (XX):

in the formula (XX): R³⁰, R³², R³³ and R³⁴represent—C_(i)H_(j)O_(k)N_(l) (where i=1 to 10, j=0 to 26, k=0 to 5,and l=0 to 5), and R³¹ represents—C_(i)H_(j)O_(k)N_(l) (where i=0 to 10,j=0 to 26, k=0 to 5, and l=0 to 5).

In one specific solvent, the reactive amine may be piperazine,N-2-Hydroethyl Piperazine, 2-aminomethyl piperazine or mixture thereof

In one illustrative solvent, one of one specific solvent components canbe represented by polyethylene glycol (PEG) represented by the followingformulae (XXI) and/or physical pressure driven solvent or mixturethereof:

Polyethylene Glycol (C_(2n)H_(4n+2)O_(n+1)) H—(O—CH₂—CH₂)_(n)—OH

where, n=integer

Glycols suitable with specific embodiments include monoethylene glycol(EG), Diethylene Glycol (DEG), Triethylene Glycol, Tetraethylene Glycol,Methoxytriglycol (MTG). Other physical solvent used as a solventcomponent are Sulfolane, N-Methyl-2-Pyrrolidone (NMP).

In one specific solvent, alkanolamines may be contained in an amount ina range from equal to or larger than 10 wt % to equal to or less than 40wt %, reactive amines may in an amount in a range from equal to orlarger than 6 wt % to equal to or less than 40 wt %, and a total amountof the alkanolamine and reactive amines may be more than 20 wt % toequal to or less than 80 wt %.

In one specific solvent, the alkanolamine may be represented by theformula (I), where each of R¹ and R² is H.

In one specific solvent, the alkanolamine may be represented by theformula (I), where x is 2 to 4 and y is 4 to 8.

In one specific solvent, alkanolamines may be represented by the formula(I), where R¹ is H and R² is —CmHnOoNp (where m=1 to 5, n=1 to 11, o=0to 5, and p=0 to 5).

In one specific solvent, the alkanolamine may be represented by theformula (I), where x is 2 to 4, y is 4 to 8, and R² is CH₃, C₂H₅, C₃H₇,or C₄H₉.

In one specific solvent, the alkanolamine may be represented by theformula (I), where R1 and R² represent —CmHnOoNp (where m=1 to 5, n=1 to11, o=0 to 5, and p=0 to 5).

In one specific solvent, the alkanoamine may be represented by theformula (I), where x is 2, y is 4, R¹ is CH₃, and R² is C₂H₄OH.

An absorbent liquid for absorbing CO₂ or H₂S or both from gas accordingto certain embodiments includes a cyclic amine compound having onenitrogen in a ring. In one specific solvent, the cyclic amine having onenitrogen in a ring may be a cyclic amine having one nitrogen in a5-membered ring, 6-membered ring, or 7-membered ring.

In one specific solvent, the cyclic amine having one nitrogen in a5-membered ring, 6-membered ring, or 7-membered ring may be pyrrolidine(PR), piperidine (PZ), or hex amethyleneimine (HMI).

In one specific solvent, the cyclic amine compound having one nitrogenin a ring may be a nitrogen containing compound having a primarynitrogen in a substituent group branching from the ring.

In one specific solvent, the nitrogen-containing compound having aprimary nitrogen in a substituent group branching from the ring may beaminomethylpiperidine or aminoethylpiperidine.

In one specific solvent, the cyclic amine compound having one nitrogenin a ring may be a nitrogen-containing compound having a hydroxyl groupin a 5-membered ring, 6-membered ring, or 7-membered ring.

In one specific solvent, the nitrogen-containing compound having ahydroxyl group in a 5-membered ring, 6-membered ring, or 7-membered ringmay be piperidinol (PDN).

An absorbent liquid includes a mixture of one specific solvent, and analkanolamine. In one specific solvent, the alkanolamine may bemonoethanolamine (MEA), ethylaminoethanol (EAE), triethanolamine,N-methyldiethanolamine (MDEA), diisopropanolamine, diglycolamine, or amixture thereof.

An process for removing CO₂ or H₂S or both a includes an absorptiontower that allows gas containing CO₂ or H₂S or both and an absorbentliquid to be in contact with each other to remove CO₂ or H₂S or bothfrom the gas; and a regeneration tower that regenerates a solution whichhas absorbed the CO₂ or H₂S or both, the absorption tower reusing thesolution regenerated at the regeneration tower by removing the CO₂ orH₂S or both from the solution.

In one embodiment, one specific solvent for recovery of carbon dioxidefrom gaseous mixture includes hindered amine, reactive amine,Polyethylene glycol, and a alkali carbonate buffer. The remainingsolvent may be water.

Reactive amines may be a piperazine and its derivative such aspiperazine, 2-aminomethyl piperazine, aminoethylpiperazine,hydroxyethylpiperazine, 3-(3-pyrrolidyl)piperidine,2-(3-pyrrolidyl)piperazine, 3-(3-piperidyl)-piperidine,3-(2-piperazinyl)piperidine, or 2-(2-piperazinyl)piperazine,2-aminomethyl piperazine. The reactive amine may be ethylenediamine,dimethyl ethylenediamine, pyrazolidine, imidazolidine,2-(2-pyrrolidyl)-pyrrolidine, 2-(2-imidazolidyl) imidazolidine ormixture thereof. One example includes a solvent having hindered amine,mixture of active amine piperazine and N-2 Hydroethyl Piperazine, acarbonate buffer, polyethylene glycol, and water.

One embodiment may include a solvent with poly ethylene glycol, any of aclass of organic compounds belonging to the alcohol family; in themolecule of a glycol, two hydroxyl (OH) groups are attached to differentcarbon atoms. The term is often applied to the simplest member of theclass, ethylene glycol. Ethylene glycol, also called 1,2-ethanediol,molecular formula HOCH₂CH₂OH, is a colourless, oily liquid possessing asweet taste and mild odor. It can be produced commercially from ethyleneoxide, which is obtained from ethylene. Further, propylene glycol, alsocalled 1,2-propanediol, resembles ethylene glycol in its physicalproperties. Other glycols include 1,3-butanediol, 1,4-butanediol,2-ethyl-1,3-hexanediol, and 2-methyl-2-propyl-1,3-propanediol,methoxytriglycol and others and are suitable herewith.

One specific solvent may contain hindered or tertiary amines that act ashigh CO₂ loading carrier as the base solvent to increase the capacity ofthe CO₂ capture solvent. Hindered amine/tertiary amine may beN-methyldiethanolamine (MDEA), 2-(2-aminoethoxy)ethanol,Aminoethylethanolamine (AEEA), 2-amino-2methyl-1-proponal (AMP),2-(ethyamino)-ethanol (EAE), 2-(methylamino)-ethanol (MAE),2-(diethylamino)-ethanol (DEAE), diisopropanolamine (DIPA),methylaminopropylamine (MAPA), 3-aminopropanol (AP), 2,2-dimethyl-1,3-propanediamine (DMPDA), 3-amino-1-cyclohexylaminopropane (ACHP),diglycolamine (DGA), 1-amino-2-propanol (MIPA), 2-methyl-methanolamine(MMEA); Di ethyl ethanol amine (DEEA)

One specific solvent may contain a carbonate buffer. The pH may rangefor a carbonate buffer may be between 8.0 and 9.0. Carbonate in onespecific solvent increases the pH of one specific solvent. This high pHallows for increased carbon dioxide capture in the form of bicarbonatesalts. The carbonate can be regenerated when one specific solvent isheated. In some instances percarbonate may contribute to the buffersystem.

Suitable carbonate buffer salts are described herein. The amount ofcarbonate buffer salt used in the buffer system is an amount that issufficient, when used with the remaining components, to raise salivarypH to a pH of about 7.8 or more, about 8.5 or more, and about 9 or more(e.g., about 9-11), irrespective of the starting pH.

In another embodiment, the carbonate salt is selected from the groupconsisting of sodium carbonate, potassium carbonate, calcium carbonate,ammonium carbonate, and magnesium carbonate. In yet another embodiment,the bicarbonate salt is selected from the group consisting of sodiumbicarbonate, potassium bicarbonate, calcium bicarbonate, ammoniumbicarbonate, and magnesium bicarbonate. In one embodiment, the binarybuffer system comprises sodium carbonate and sodium bicarbonate. Inanother embodiment, the sodium bicarbonate is dessicant-coated sodiumbicarbonate.

The amount of carbonate buffer and reactive amine piperazine in thesolution is limited by the solubility of both components in water, thusresulting in solid solubility limit for aqueous solutions. At 25 C, thesolubility of potassium carbonate buffer in a CO₂ rich solution is 3.6 mand the solubility of piperazine in water is approximately 2 m. With thesolid solubility limitation, the resulting lower concentration canresult in slow reaction rate and low solution capacity. By combiningpiperazine and carbonate buffer solubility in polyethylene glycol andaqueous solutions, the resultant solubility increases.

Reactive amines such as piperazine and CO₂ react, it undergoesequilibrium reaction to form piperazine carbamate and piperazinedicarbamate and some free and bound piperazine. Because of the additionof carbonate buffer salt; which react with free and bound piperazine inreacting more CO₂ to form piperazine carbamate and piperazinedicarbamate.

The ratio of equivalents of carbonate salt to equivalents of reactiveamine can be between 0.3-3.0. The concentrations of the reactive amineand carbonate salt can be between 3.0-8.0 equivalents/Kg H₂O or 4.0 and6.0 equivalents/Kg H₂O. The amount of piperazine and carbonate buffersalt can be adjusted based on the solubility in water and polyethyleneglycol.

In one example, one specific solvent and method of use for the removalof CO₂ from flue gas, natural gas, hydrogen gas, synthesis gas, andother process and waste gas streams. One specific solvent may contain acarbonate buffer, a reactive amine, a hindered amine, and a polyethyleneglycol, resulting in the solution pH between (10-13.5) in absence ofCO₂. The reactive amine 6 wt % to 40 wt % with the total concentrationlimited by the solid solubility of the reactive amine in aqueous andpolyethylene glycol solution or of the carbonate buffer salt from 0.15wt %-10 wt % with total concentration limited by the solid solubility inaqueous solution. This chemical solvent is designed to increase the rateof CO₂ removal to improve the efficiency of a removal process.

Piperazine is freely soluble in water and solubility in ethylene glycolup to a about 20 wt %. Carbonate buffer salt solubility in water is 112g/100 mL at 20° C.,

The temperature of the solution when contacting with the gaseous streammay be between approximately 30 C-125 C. The rate constant for thereaction of CO₂ with the piperazine derivative (K_(PZ)) may be at least25 m³/mol-s at 25 C, or at least 50 m³/mol-s at 25 C.

In one embodiment, one specific solvent has a reactive amine inconcentration between about 6 wt % and 40 wt %.

In yet another embodiment, one specific solvent has a alkanolamine in aconcentration between about 10 wt % and 40 wt %.

In yet another embodiment, one specific solvent has a carbonate bufferhas concentration between about 0.15wt %-10 wt %.

In yet another embodiment, one specific solvent has a soluteconcentration between about 2 wt %-40 wt %.

In yet another embodiment, one specific solvent has a tertiary balanceto keep one specific solvent or solvent system as a single liquid phase.

In yet another embodiment, the solvent the alkanolamine has a weightpercentage between 25 wt % and 40 wt % and is selected from groupcomprising N-methyldiethanolamine (MDEA), 2-amino-2methyl-1-proponal(AMP); the reactive amines have a weight percentage between 10 wt % and25 wt % and is selected from group comprising piperazine, Naminoethylpiperazine (AEP); and the glycol has a weight percentagebetween 10 wt % and 25 wt %.

In yet another embodiment, the solvent the alkanolamine has a weightpercentage between 30 wt % and 40 wt % and is selected from groupcomprising N-methyldiethanolamine (MDEA), 2-amino-2methyl-1-proponal(AMP); the reactive amines have a weight percentage between 10 wt % and18 wt % and is selected from group comprising piperazine, Naminoethylpiperazine (AEP); and the glycol has a weight percentagebetween 15 wt % and 20 wt %.

In yet another embodiment, the solvent the alkanolamine has a weightpercentage between 32 wt % and 35 wt % and is selected from groupcomprising N-methyldiethanolamine (MDEA), 2-amino-2methyl-1-proponal(AMP); the reactive amines have a weight percentage between 11 wt % and15 wt % and is selected from group comprising piperazine, Naminoethylpiperazine (AEP); and the glycol has a weight percentagebetween 18 wt % and 20 wt %.

In yet another embodiment, the solvent the alkanolamine has a weightpercentage between 25 wt % and 40 wt %; the reactive amines have aweight percentage between 10 wt % and 25 wt %; and the glycol has aweight percentage between 10 wt % and 25 wt %.

In yet another embodiment, the solvent the alkanolamine has a weightpercentage between 30 wt % and 40 wt %; the reactive amines have aweight percentage between 10 wt % and 18 wt %; and the glycol has aweight percentage between 15 wt % and 20 wt %.

In yet another embodiment, the solvent the alkanolamine has a weightpercentage between 32 wt % and 35 wt %; the reactive amines have aweight percentage between 11 wt % and 15 wt %; and the glycol has aweight percentage between 18 wt % and 20 wt %.

In yet another embodiment, the solvent the alkanolamine has a weightpercentage between 25 wt % and 40 wt %; the reactive amines have aweight percentage between 10 wt % and 25 wt %; and the sulfolane has aweight percentage between 10 wt % and 25 wt %.

In yet another embodiment, the solvent the alkanolamine has a weightpercentage between 30 wt % and 40 wt %; the reactive amines have aweight percentage between 10 wt % and 18 wt %; and the sulfolane has aweight percentage between 15 wt % and 20 wt %.

In yet another embodiment, the solvent the alkanolamine has a weightpercentage between 32 wt % and 35 wt %; the reactive amines have aweight percentage between 11 wt % and 15 wt %; and the sulfolane has aweight percentage between 18 wt % and 20 wt %.

In another embodiment, a method of removing CO₂ from a gaseous streamincluding: contacting a gaseous stream with a solution wherein thesolution is formed by combining: alkanolamines, a reactive amine, ancarbonate salt, poly ethylene glycol and water; whereby the contactremoves CO₂ from the gaseous stream; and regenerating the solution. Theconcentrations may be limited by the solubility of the components at atemperature and contact of the exhaust gaseous stream with one specificsolvent removes CO₂ from the gaseous stream; and regenerating thesolution.

The regenerating may include heating CO₂-rich solution, which may occurat a temperature of approximately 90 C-130 C, approximately 110 C. Anadditive such as an antifoaming agent, an antioxidant, a corrosioninhibitor (e.g. vanadium oxide or a chromate), a flocculation aid, or amixture of two or more additives may be included as part of thesolution.

In another embodiment, the method of removing CO₂ from a gaseous streammay further include applying a water wash system, wherein the water washsystem collects the volatile alkanolamine and reactive amine fromtreated gaseous stream. The regeneration of the solution may occur in avacuum stripper column, and the solution may be returned to contact withthe gaseous stream after regeneration.

Other components of a gaseous stream, such as COS may also be removed bythe method of this disclosure. The gaseous stream may be from acoal-fired power plant, or it may be flue gas, natural gas, hydrogengas, synthesis gas or a waste gas stream.

FIG. 2 is a schematic diagram of an apparatus for removing acidic gasesespecially CO₂. As shown in FIG. 2, gas is allowed to enter to anabsorption tower 1 through a CO₂—containing gas-feed. In a packedportion, the gas placed in the absorption tower 1 is brought intocontact in a counter flow with a CO₂ absorbent liquid fed from 3, andCO₂ is absorb and removed from the gas by the absorbing liquid, and theresultant gas is discharge from the top as treated gas. The absorbentliquid fed to the absorption tower 1 absorb CO₂, and is led to heatexchanger and heated and led to a regeneration tower 4. In theregeneration tower 4, the absorbent liquid flows through a packedportion towards the lower portion of the tower. During this time, CO₂ isremoved to regenerate the absorbent liquid. The regenerated absorbentliquid is led by a pump to the heat exchanger and fed back to theabsorption tower 1 through an absorbent liquid feed inlet line 3.

On the other hand, in the upper portion of the regeneration tower 4, theCO₂ removed from the absorbent liquid is brought into contact with areflux water, and cooled by a regeneration tower reflux condenser and,in a reflux drum, the CO₂ separated from the reflux water formed bycondensing water vapor accompanying the CO₂, and led to a CO₂ recoverystep. The reflux water is fed by a reflux water pump to the regeneratortower 4. This embodiment briefly describes an overview of the CO₂capture process description.

Illustrative Examples and Proposed Theory

Heat to produce steam to maintain driving force for CO₂, For the CO₂, tobe transferred from the liquid to the gas phase there needs to bedriving force on the basis of partial pressure. Thus, steam acts in sucha way as to provide this driving force so that the mass transfer of CO₂from the liquid to the gas phase is enhanced. This also has energyassociated with it, which contributes to the overall reboiler duty. Thiscan be obtained by finding out the amount of water associated with thepure CO₂ steam produced as this energy in the form of water is lost andneeds to be provided by the reboiler. The stripping heat consists of thefollowing:

Q _(T) =Q _(sens) +Q _(des) Q _(strip)

Sensible Heat of CO₂ Rich Solvent to Raise the Stripper Temperature

One specific solvent loaded with CO₂ in the absorber may be heated up tostripper temperature for the regeneration of CO₂. One specific solventstream can be pre-heated in the lean-rich cross heat exchanger and thenadditional heat may be used to maintain the temperature of one specificsolvent in the stripper.

$Q_{sens} = \frac{\delta \; C_{P}\Delta \; T}{\left( {\alpha_{rich} - \alpha_{lean}} \right)C_{amine}}$

The contributing factors to the sensible heat are solvent flow, specificheat capacity of one specific solvent and the temperature increase.Thus, the only parameter that can be varied is one specific solvent flowwhich further depends on the concentration of one specific solvent andone specific solvent loadings. This can be decreased by circulating lesssolvent and maintaining the same CO₂ production rate. This is checked bymeans of comparing the Net Capacity of a solvent which is defined as thedifference in the loading at the absorption and desorption conditions.

Heat of Desorption of CO₂

The CO₂ which is reversibly bound to one specific solvent needs to beregenerated. The heat of desorption is equivalent to the heat ofabsorption.

Heat to Produce Steam to Maintain Driving Force for CO₂

For the CO₂ to be transferred from the liquid to the gas phase thereneeds to be driving force in the basis of the partial pressure. Thussteam acts in such a way as to provide the driving force so that themass transfer of CO₂ from the liquid to the gas phase is enhanced. Thisalso has energy associated with it, which contributes to the overallreboiler duty. This can be obtained by finding out the amount of waterassociated with the pure CO₂ steam produced as this energy in the formof water is lost and needs to be provided by the rebuilder. Thestripping heat consists of the following:

$Q_{strip} = {\frac{{P_{H\; 2\; O}^{sat}\left( T_{{top},{des}} \right)}\chi_{{H\; 2\; O},{freebasis}}}{P_{{CO}\; 2}^{*}\left( {T_{{top},{des}} \cdot \alpha_{rich}} \right)}\Delta \; H_{H\; 2\; O}^{vap}}$

Where ΔH_(H2O) ^(vap) stands for heat of vaporization if water andP*_(CO2) is the partial pressure of CO₂ that would be equilibrium withthe rich solution at the bottom of the absorber. Thus, finding

EXAMPLES

The disclosure will be further described in connection with thefollowing examples, which are set forth for purposes of illustrationonly.

TABLE 1 Methoxytri Sulfolane EG NMP DEG glycol Molecular kg/kmol 120.262.1 99.1 106.1 164.2 Weight Mass Cp kJ/(kg * ° C.) 1.2319 2.4734 1.61812.3353 2.19 Dynamic cP 7.9380 9.5081 1.4516 15.3050 7.3000 ViscosityLatent Heat of kJ/kg 435.11 849.57 453.74 540.63 301.00 vaporizationBoiling Point Deg C. 289.933 197.080 203.994 244.938 249.000

As the rate activator for the CO₂ absorption is piperazine and itsderivative, the limitation with piperazine is its high volatility. Ithas highest reaction kinetics among its derivatives. It is whitecrystals which need more water to foam a clear solutions or needPolyethylene glycol to solubilize it. But because of the high volatilitythe loss of the piperazine is high and to minimize the volatility lossin the solvent, piperazine component is partly or completely replaced byrate activator such as N-2-hydroethyl piperazine whose vapor pressure is99.7% less than piperazine.

N-2-HYDROETHYL Reactive Amine Piperazine Piperazine Formula C4H10N2C6H14N2O Mol. Wt 84.16 130.19 State SOLID LIQUID Appearances WHITE LIGHTYELLOW CRYSTAL M.pt (deg C.) 106 −10 B.pt (deg C.) 146 246 Solubility(water) SOLUBLE SOLUBLE Vapor pressure 2.1 AT 20 C. 0.00492 AT 25 C.(mmHg) Acidity pKa 9.8

Example 2

Below is the composition and characteristics of another exemplarysolvent.

Density Measurement

The densities of were measured using a 25×10 ⁶m³ (at 298 K) Gay-Lussacpycnometer. For each run, the pycnometer containing the solvent solutionwas put in a constant temperature bath. The bath temperature wascontrolled within ±0.1 K of the desired temperature level using acirculator temperature controller. Once the solution reached the desiredtemperature, it was weighed to within ±0.0001 g with an analyticalbalance. Each reported density data is the average of at least threemeasurements.

Viscosity Measurement

The viscosities of solutions were measured using Cannon FenskeViscometer. For each viscosity measurement, the temperature wascontrolled within ±0.1 K of the desired level with a circulatortemperature controller. The viscometers containing samples were immersedin a thermostatic bath and allowed to equilibrate to the set pointtemperature for at least 15 min. Later, the efflux time of samples wasmeasured manually with a digital stopwatch having an accuracy of 0.01 s.The efflux time is measured by allowing meniscus to pass between twospecific marks. The kinematic viscosity was obtained by multiplyingefflux time in seconds with the respective viscometer constant. Thedynamic viscosity of the samples is calculated by multiplying thekinematic viscosity values with their corresponding density values. Eachviscosity data is the average of at least three measurements.

Molality Molarity (mol/kg Density Mass % Mol % (mol/lit) water) Kg/m³MDEA 25 7.3 2.185 5.387 1055 at 40° C. Ethylene Glycol 20 11.19 3.3518.262 Piperazine 15 6.05 1.811 4.465 K₂CO₃ 1 0.25 0.0734 0.186 H₂O 3975.21

Density and Viscosity of S1:

Temp viscosity density C. m-Pa-sec kg/m3 30 10.16252 1065 40 6.9626531055 50 4.170193 1048 60 2.777815 1040FIG. 3 describes viscosity in mPa·sec and density in kg/m³ (on Y-axis)w.r.t. temperature ° C. (on X-axis) for the solvent S₁. It is observedthat viscosity and density decreases with the increase in temperature.

VLE of S₁

These measurements can determine the relationship between partialpressure of CO₂ and the subsequent loading of the solvent at differenttemperatures. This data can be used to do a first assessment of thesolvent performance.

T = 40° C. CO₂ PARTIAL Loading pressure kPa 0.118545 0.068 0.1673150.208 0.20191 0.420 0.231713 0.963 0.27593 2.388 0.315874 5.076 0.3561948.245 0.395963 14.492 0.470479 33.408 0.496462 50.479 0.539315 78.0510.575544 98.729

T = 50° C. CO₂ PARTIAL (Loading pressure kPa 0.067229 0.043 0.1196260.159 0.189261 0.710 0.232958 1.701 0.287389 4.549 0.320698 7.5130.379275 16.116 0.400526 24.539 0.484553 62.484 0.516075 76.269 0.528049103.841

Kinetics Experiments Results

Mass % MDEA 25 Ethylene Glycol 20 Piperazine 15 K₂CO₃ 5 H₂O 35

Pressure Rate kPa kmol/m² · s 3.64 4.89E−06 7.62 8.82E−06 15.7 9.85E−06Specific rate of absorption increases with CO₂ partial pressure.

Example 3

Below is the composition and characteristics of another exemplarysolvent.

VLE Data for Solvent S2

(MDEA+PZ+Tetrahydrothiophenedioxide (SULFOLANE) +water (and K2CO3))(48+2+10+40 wt %, respectively)

T = 313 K T = 323 K T = 333 K p_(CO) ₂ /kPa α_(CO) ₂ p_(CO) ₂ /kPaα_(CO) ₂ p_(CO) ₂ /kPa α_(CO) ₂ 2.07 0.108 26.88 0.263 41.28 0.249 28.950.362 82.71 0.474 192.63 0.464 53.76 0.493 261.78 0.708 343.84 0.63693.05 0.633 506.91 0.868 616.88 0.754 254.35 0.790 677.88 0.946 855.130.894 496.29 0.934 856.09 1.020 1082.87 0.996 622.43 0.997 955.89 1.0871127.33 1.062 756.84 1.032 1355.41 1.120 955.89 1.110

VLE Data for (MDEA+PZ+SULFOLANE+(H₂O and K2CO3)) (45+5+10+40 wt %,Respectively)

T = 313 K T = 323 K T = 333 K p_(CO) ₂ /kPa α_(CO) ₂ p_(CO) ₂ /kPaα_(CO) ₂ p_(CO) ₂ /kPa α_(CO) ₂ 39.29 0.381 6.20 0.112 39.90 0.282 97.190.637 86.85 0.488 125.50 0.492 328.79 0.876 225.45 0.735 308.66 0.668554.92 0.984 492.84 0.915 458.63 0.795 812.58 1.068 622.91 0.989 630.560.860 1046.34 1.132 851.53 1.044 834.36 0.954 1022.51 1.079 1070.161.048 1104.77 1.094 1334.16 1.157 1292.37 1.137VLE Data for (MDEA+PZ+SULFOLANE+Water(and K₂CO₃)) (42+8+10+40wt %,Respectively)

T = 313 K T = 323 K T = 333 K p_(CO) ₂ /kPa α_(CO) ₂ p_(CO) ₂ /kPaα_(CO) ₂ p_(CO) ₂ /kPa α_(CO) ₂ 1.24 0.236 5.38 0.321 16.80 0.264 16.180.503 49.49 0.567 65.72 0.455 94.38 0.750 101.33 0.671 174.93 0.615192.78 0.855 145.10 0.738 326.32 0.805 223.33 0.895 274.27 0.848 497.350.898 465.28 1.004 332.93 0.860 670.47 0.936 599.69 1.082 545.93 0.973833.25 0.997 777.53 1.144 779.60 1.075 1095.73 1.069 976.05 1.169 984.321.130 1164.45 1.091 1013.27 1.182

1. A solvent for recovery of carbon dioxide from gaseous mixture, comprising: (a) an alkanolamine, (b) reactive amines, (c) a carbonate buffer, wherein one specific solvent contains less than about 75% by weight of water and has a single liquid phase.
 2. The solvent as claimed in claim 1, further comprising a glycol.
 3. The solvent as claimed in claim 2, wherein the glycol is poly ethylene glycol.
 4. The solvent as claimed in claim 1, further comprising a sulfolane.
 5. The solvent as claimed in claim 2, wherein the glycol is selected from the group consisting of monoethylene glycol (EG), Diethylene Glycol (DEG), Triethylene Glycol, Tetraethylene Glycol, Methoxytriglycol (MTG). Other physical solvent used as a solvent component are Sulfolane, N-Methyl-2-Pyrrolidone (NMP).
 6. The solvent as claimed in claim 1 or 3, the solvent is 4less than about 30% by weight of water.
 7. The solvent as claimed in claim 1 or 3, wherein the carbonate buffer is a potassium carbonate buffer.
 8. The solvent as claimed in claim 1, wherein the promoter is 2% and 30% wt percent.
 9. The solvent as claimed in claim 1 or 3, wherein the alkanolamine is comprises at least one amine of the formula (I), (II), (III) where x and y respectively satisfy relationship: 1 less than or equal to 5 and 2 less than or equal to 10; and R¹, R², R³, and R⁴ represent—C_(i)H_(j)O_(k)N_(l) (where i=0 to 10, j=1 to 21, k=0 to 5, and l=0 to 5).


10. The solvent as claimed in claim 1 or 3, wherein the alkanolamine is selected from group comprising N-methyldiethanolamine (MDEA), 2-(2-aminoethoxy)ethanol, Aminoethylethanolamine (AEEA), 2-amino-2methyl-1-proponal (AMP), 2-(ethyamino)-ethanol (EAE), 2-(methylamino)-ethanol (MAE), 2-(diethylamino)-ethanol (DEAE), diisopropanolamine (DIPA), methylaminopropylamine (MAPA), 3-aminopropanol (AP), 2,2-dimethyl-1,3-propanediamine (DMPDA), 3-amino-1-cyclohexylaminopropane (ACHP), diglycolamine (DGA), 1-amino-2-propanol (MIPA), 2-methyl-methanolamine (MMEA), diethyl ethanol amine or any combinations thereof at concentration ranging from about 20 wt % to about 45 wt %. The solvent as claimed in claim 1, wherein the reactive amine is selected from group comprising piperazine, N-aminoethylpiperazine (AEP), N-methylpiperazine, 2-methylpiperazine, 1-ethylpiperazine, 1-(2-hydroxyethyl) piperazine, 2,5-dimethylpiperazine , 1-Amino-4-Methyl Piperazine and any combinations thereof.
 11. The solvent as claimed in claim 1, wherein the reactive amine is greater than 6% by weight and buffers the solution to a pH of between about 12 and 14 in the absence of CO₂.
 12. The solvent as claimed in claim 1, wherein (a) the alkanolamine has a weight percentage between 25 wt % and 40 wt % selected from group comprising N-methyldiethanolamine (MDEA),2-amino-2methyl-1-proponal (AMP), (b) reactive amines have a weight percentage between 10 wt % and 25 wt %, selected from group comprising piperazine, N aminoethylpiperazine (AEP), (c) glycol has a weight percentage between 10 wt % and 20 wt %.
 13. The solvent as claimed in claim 1, wherein (a) the alkanolamine has a weight percentage between 30 wt % and 40 wt % selected from group comprising N-methyldiethanolamine (MDEA),2-amino-2methyl-1-proponal (AMP) (b) the reactive amines have a weight percentage between 10 wt % and 18 wt %, selected from group comprising piperazine, N aminoethylpiperazine (AEP) (c) the glycol has a weight percentage between 15 wt % and 20 wt %.
 14. The solvent as claimed in claim 13, wherein the glycol is poly ethylene glycol.
 15. The solvent as claimed in claim 3, wherein (a) the alkanolamine has a weight percentage between 25 wt % and 40 wt % selected from group comprising N-methyldiethanolamine (MDEA), 2-amino-2methyl-1-proponal (AMP), (b) reactive amines have a weight percentage between 10 wt % and 25 wt %, selected from group comprising piperazine, N aminoethylpiperazine (AEP), (c) the sulfolane has a weight percentage between 10 wt % and 20 wt %.
 16. The solvent as claimed in claim 1, wherein (a) the alkanolamine has a weight percentage between 32 wt % and 35 wt % selected from group comprising N-methyldiethanolamine (MDEA),2-amino-2methyl-1-proponal (AMP), (b) reactive amines have a weight percentage between 11 wt % and 15 wt %, selected from group comprising piperazine, N aminoethylpiperazine (AEP), (c) poly ethylene glycol has a weight percentage between 18 wt % and 20 wt %.
 17. A method for removing CO₂ from a stream, comprising the steps of: (a) contacting the stream with a solvent having an alkanolamine, rate activator amines, glycol or sulfanone, and a carbonate buffer; (b) allowing one specific solvent to absorb CO₂ at a temperature ; (c) regenerating one specific solvent from heating one specific solvent greater than
 80. 18. The method as claimed in claim 17, wherein the stream has a temperature between 40 C to 65 C.
 19. The method as claimed in claim 17, wherein the alkanolamine compounds of the formula (I) include monoethanolamine (MEA), methyldiethanolamine (MDEA), diethanolamine (DEA), triethanolamine (TEA), diisopropanolamine (DIPA), 2-amino-1-propanol (AP), 2-amino-2-methylpropanol (AMP), ethyldiethanolamine (EDEA), 2-methylaminoethanol (MEA), 2-ethylaminoethanol (EAE), 2-n-propylaminoethanol, 2-nbutylaminoethanol (n-BAE), 2-n pentylaminoethanol, 2-isobutylaminoethanol (IBAE), 2-dimethylaminoethanol (DMAE) and 2-diethylaminoethanol (DEAE), alkanolamine compounds of the formula (II) include 2,3-diaminopropionic acid (DAPA) and glycine and alkanoamine compounds of the formula (III) include 1,2 ethylenediamine.
 20. The solvent as claimed in claim 17, wherein (a) the alkanolamine has a weight percentage between 32 wt % and 35 wt % selected from group comprising N-methyldiethanolamine (MDEA),2-amino-2methyl-1-proponal (AMP), (b) reactive amines have a weight percentage between 11 wt % and 15 wt %, selected from group comprising piperazine, N aminoethylpiperazine (AEP), (c) the glycol has a weight percentage between 18 wt % and 20 wt %.
 21. The solvent as claimed in claim 17, wherein (a) the alkanolamine has a weight percentage between 25 wt % and 40 wt % selected from group comprising N-methyldiethanolamine (MDEA), 2-amino-2methyl-1-proponal (AMP), (b) reactive amines have a weight percentage between 10 wt % and 25 wt %, selected from group comprising piperazine, N aminoethylpiperazine (AEP), (c) the sulfolane has a weight percentage between 10 wt % and 20 wt %.
 22. A method for removing CO2 from a stream, comprising the steps of: (a) contacting the stream with a solvent having components amine, glycol, reactive amine, and a carbonate buffer, wherein the solvent contains less than about 75% by weight of water, (a) allowing the solvent to absorb CO2 at a temperature, and (b) regenerating the solvent from heating the solvent greater than 80 C, wherein the stream has a temperature between 40 C to 65 C, and the regeneration is under a pressure between about 0.01 and 30 bar.
 23. The method as claimed in claim 21, wherein the amine is hindered amine. 